The zwitterion formed from triphenylphosphine and DMAD adds to electron-deficient styrenes to form stable cyclopentenyl phosphoranes. This is the first example of such a zwitterion in which the phosphine is incorporated into the product Ever since the pioneering work of Horner, 1 the zwitterion derived from triphenylphosphine and DMAD has been the subject of several investigations. 2 Following the early work of Winterfeldt, 3 Nozaki et al. have shown that the zwitterion reacts with activated carbonyl compounds to afford highly functionalized g-butyrolactones. 4 We have demonstrated that the activated carbonyl of benzoquinones can successfully take part in these reactions thus constituting a facile synthesis of spiro-fused heterocyclic compounds. 5 Noteworthy in this context is the work of Trost 6 and Lu 7 who have developed intra-as well as intermolecular two-component transformations of electrondeficient alkynes and allenes catalyzed by triphenylphosphine. In the majority of these reactions phosphine plays a catalytic role. There are also reports of reactions in which the phosphine moiety participates in an intramolecular Wittig-type reaction leading to its ejection as triphenylphosphine oxide. 8 In this paper we detail the three component reaction of triphenylphosphine, DMAD, and arylidene malononitriles yielding stable cyclopentenyl phosphoranes. 9Our studies were initiated with 4-methyl dicyanostyrene (1a) which on treatment with DMAD and triphenylphosphine in anhydrous DME as solvent at room temperature yielded a highly polar phosphorane 4a as the product within two hours in 63% yield. Similar reactivity was observed with other dicyanostyrenes and the results are summarized in Table 1.The cyclopentenyl phosphorane structure of 4a was assigned on the basis of spectroscopic analysis. The IR spectrum of 4a revealed the ester carbonyl absorption at 1743 cm -1 , while that of the cyano group was at 2242 cm -1 , and the carbonyl adjacent to cyano was observed at 1660 cm -1 . The methoxy protons of the ester group in 4a were discernible at 2.86 ppm in the 1 H NMR spectrum. The 13 C NMR signals for the carbonyls were seen at 180.8 and 165.9 ppm, the latter corresponding to that of the ester. Conclusive evidence for the structure was obtained by single crystal X-ray analysis (Figure 1). Figure 1Single-crystal X-ray structure of 4a

Alkyl isocyanides, DMAD, and various activated styrenes furnish fully substituted cyclopentadienes in a one-pot three-component reaction. [reaction: see text]

[reaction: see text] The pyridine-mediated reaction of dimethyl acetylenedicarboxylate and cyclobutene-1,2-diones affords selective access to either hexasubstituted benzene derivatives or cyclopentenedione derivatives depending on the concentration of pyridine.